The present invention relates to a gasket clamped between two members fastened by fixtures to seal a sealing subject hole, and an engine with the gasket.
In order to improve fuel consumption, in a recent engine (internal combustion), both a cylinder block and a cylinder head are formed by a lighter material, for example, aluminum and the like, or a thickness is thinly formed and the like so as to be made lighter. As a result, both the cylinder block and the cylinder head have a low rigidity.
When such a cylinder block and cylinder head are tightened by a high head-bolt axial force by clamping the cylinder head gasket for sealing a combustion gas inside a cylinder bore, coolant water inside a water jacket, and lubricant oil, since a thickness of an upper face of the cylinder block is thin, there acts a force pulling up the cylinder block near an end of a head bolt. Also, at the same time, near the sealing subject hole such as the cylinder bore and the like, there also acts a force pushing down on the cylinder block by a surface pressure of the cylinder head gasket. As a result, a stress at a periphery of the water jacket or at a periphery of the cylinder bore increases locally, and there is a problem that the cylinder bore or a cylinder liner inserted into the cylinder bore is distorted or deformed.
Especially, in a case of a closed-deck-type cylinder block, the head bolt and the cylinder bore are connected without opening, so that the stress at the periphery of the water jacket or at the periphery of the cylinder bore of the relevant portion increases. Accordingly, a distortion or a deformation of the cylinder bore or the cylinder liner tends to occur.
If the cylinder bore or the cylinder liner is distorted or deformed, and is no longer capable of maintaining a circular shape, an unnecessary resistance is generated between the cylinder bore or the cylinder liner, and a piston carrying out a piston movement inside the cylinder bore; thereby the fuel consumption is deteriorated. Also, the lubricant oil flows into the cylinder bore, and the lubricant oil burns so as to cause adverse effects on an exhaust gas.
Here, a conventional cylinder head gasket will be explained with reference to FIG. 6. A cylinder head gasket 10X is the gasket clamped between a cylinder block 2 and a cylinder head 3 fastened by head bolts 1, and sealing cylinder bores 4, water jackets 5, and a hole for the lubricant oil which is not shown in the figure. The cylinder head gasket 10X is the gasket used for, i.e., the closed-deck-type cylinder block 2 wherein all upper faces of the water jackets 5 are not open.
The cylinder head gasket 10X comprises cylinder-bore holes 12, water holes 13, and bolt holes 14 in a substrate 11 formed by laminating a plurality of metal plates. As shown in FIG. 7, in respective circumferential edge portions thereof, there are provided cylinder-bore hole beads 15, water hole beads 16, and bolt hole beads 17.
The cylinder head gasket 10X is clamped between the cylinder block 2 and the cylinder head 3, and the head bolts 1 are inserted and passed through the bolt holes 6, 7, and 14 so as to fasten the cylinder block 2 and the cylinder head 3. At that time, the cylinder block 2 and the cylinder head 3 are fastened by the high head-bolt axial force to allow the cylinder head gasket 10X to reliably seal the combustion gas inside the cylinder bores 4, the coolant water inside the water jackets 5, and the lubricant oil.
In a case of being fastened by the high head-bolt axial force in this manner, a fastening stress concentrates in areas (hereinafter, these portions are called fastening-stress concentration areas A) shown by A in the figure, and as mentioned above, the stress increases in these portions. Then, as a result, as shown in FIG. 7, inner circumferential faces 4a of the cylinder bores 4 are distorted, or the cylinder liner which is not shown in the figure is distorted.
With respect to the aforementioned problem, there is proposed a device wherein an end-surface pressure adjusting portion is provided in a gasket main body, which can press against a deck surface of the cylinder block and a deck surface of the cylinder head on an outside further than an end-portion bolt line connecting centers of a pair of bolt insertion holes lining up in a width direction of the engine at both end portions in a cylinder line direction, or in both end portions in the cylinder line direction (for example, see Japanese Patent Application Publication No. 2005-23773).
The aforementioned device can solve the problem that by the surface pressure receiving from the cylinder head gasket, the cylinder bore of each cylinder is deformed to bulge, so that if a surface pressure distribution is uneven, a deformation amount of the cylinder bore becomes also uneven so as to impair a circularity of the cylinder bore. Accordingly, the deformation of the cylinder bore relevant to the cylinder line direction can be controlled.
However, as mentioned above, when the cylinder block and the cylinder head are fastened, the fastening-stress concentration areas wherein the fastening stress thereof concentrates are generally disposed in a radial direction relative to the cylinder bore. Therefore, the deformation of the cylinder bore occurs not only in the cylinder line direction.
Also, the surface pressure distribution in a whole area of the gasket is made symmetrical in a right-and-left direction so as to control the deformation of the gasket cylinder bore in the cylinder line direction. However, there is no effect on the deformation of each cylinder bore due to the fastening stress in the fastening-stress concentration areas present in an outer circumference of each cylinder bore, and the distortion or the deformation of each cylinder bore cannot be controlled.
The present invention is made in view of the aforementioned problem, and an object of the present invention is to provide a gasket and a cylinder head gasket which can reduce the fastening stress generated when the two members are fastened by the fixture, and control the distortion, the deformation, or the like due to the fastening stress.
Further objects and advantages of the invention will be apparent from the following description of the invention.